Become a fan of Slashdot on Facebook

 



Forgot your password?
typodupeerror
DEAL: For $25 - Add A Second Phone Number To Your Smartphone for life! Use promo code SLASHDOT25. Also, Slashdot's Facebook page has a chat bot now. Message it for stories and more. Check out the new SourceForge HTML5 Internet speed test! ×

Comment Re:The problem (Score 1) 145

Quads can't, no variable pitch blades.

And you don't see the solution to that?

It's really simple. Regulators mandate safety standards so that - in real world conditions - you don't have cars constantly falling out of the sky due to failures or running into buildings. Engineers determine the designs to meet those standards. If they can't, they don't get to sell it.

Comment Re:I agree, but not for the same reasons as Musk (Score 1) 145

Congratulations, you have it entirely backwards.

The maximum efficiency of a prop, in newtons per watt, is 1 / (v_wake + v_freestream), where velocity is in meters per second. The faster you're moving (the freestream velocity), the less thrust you get per watt. Which is why large props are more efficient (more air moved at a lower wake speed), particularly at low speeds, and same for high bypass jet engines.

Now, in terms of "energy per 100km" or "miles per unit energy", obviously a hover yields "infinite joules per 100km" and "0 miles per joule", because you're not going anywhere. But that's an entirely different situation than propulsive efficiency. If you want to start factoring in motion, then your cross section / drag coefficient / L:D ratio / altitude (and thus density) and so forth come into play, and the optimum speed comes down to a balance between a wide range of factors - the faster you go, the less time you spend flying, but your drag increases quadratically, and your prop efficiency drops (the rate of drop relative to the difference between the freestream and wake velocities). Airplanes maximize this balancing point by having extremely low drag coefficients (Cd), far less than cars tend to have.

Comment Re:Really? (Score 1) 145

The assumption is that if flying cars were common, there would be vastly more locations. As they basically function like helicopters (in most conceptions - VTOL), they need only something equivalent to a helipad, not an airport. Which is much cheaper and smaller footprint than an airport.

To get to the point of allowing takeoff and landing from, say, a driveway, you'd have to have a long track record of excellent proven safety, and levels of noise reduction that current technology doesn't yet support. It's certainly conceivable in the future, but is anything but a first step for companies working on flying cars today.

I personally view flying cars as pretty much inevitable (although not around the corner) regardless of whether or not they're pursued directly at present. Namely because of delivery drones. Businesses are not going to stop pushing for them because there's such an economic case for them (not having to drive a big truck around city streets, pairing trucks with drones to not have to go down each sidestreet or stop at each location, etc), and they'll advance the technology as needed to get approval - starting small. But economics will continually push them toward making larger and larger models, and the technology to get approval for those. And eventually you'll have models large enough to carry people around, wherein the question will inherently arise, "Why, exactly, aren't they carrying people?"

Comment Re:Really? (Score 1) 145

So your concept is that something statistically likely to crash and injure people would be approved by regulators, rather than manufacturers being forced to prove reliability in real-world usage conditions before being granted approval?

Comment Re:Really? (Score 0) 145

The assumptions involved in your post:

1) Flying cars would be allowed to just take off and land wherever they want.
2) People would be manually piloting them.

I don't know where you're getting your concept of flying cars, but none of the flying car advocates I've ever heard from advocate for either of those things.

Comment Re:The problem with flying cars is... (Score 2) 145

I don't want to think of what they would be like as pilots

Yes, because when people talk about flying cars, they totally mean manual piloting.

I don't even want to consider those traffic jams.

Um...

Waterfall Sr.: Our peace ring has 'em trapped like a tiger in a washing machine!
[The engine of the Planet Express ship flares up.]
Leela: Get ready!
Protestor #1: Look out!
Protestor #2: Hold on!
Waterfall Sr.: Here they come!
[The ship rises up from the middle of the peace ring and tows the tanker over the top of the protestors. It flies away.]
Leela: When you were planning this peace ring, didn't you realise spaceships can move in three dimensions?
Waterfall Sr.: No, I did not.

Comment Re:Speaking of delays... (Score 1) 107

ULA's track record with the Atlas V: 100%

Yes, let's take one vehicle in its fifth generation (not counting subrevisions), and ignore its track record with all of its earlier versions that led up to this point and all of their failures, and all of Lockheed and Boeings' other launch vehicles over time, with all of their failures. Lets also ignore that they're going to have to switch engines soon, to an engine with zero track record.

Payloads typically launch on schedule or within a few weeks. .... Some payloads have been waiting literally years due to delays.

Let's totally ignore that Atlas V launches once per two months, while SpaceX launches once per month, and that almost all of the wait time was due to investigation backlog. When it comes to hitting launch windows, SpaceX has a higher average success rate than average than Atlas V

And lets entirely fail to mention the point that ULA charges nearly double what SpaceX does per kilogram. Or that SpaceX is doing everything while rapidly evolving its rocket, to the point that they've basically even switched propellants partway through (denisification radically changes their properties). And while at the same time running an aggressive recovery and refurbishment programme and developing a heavy lift vehicle, with a small fraction as much capital.

Comment Re:What governmen brought to the table (Score 1) 107

As if liquid boosters can't fail catastrophically? Check out SpaceX's last failure. Liquids are hardly immune to catastrophic failure.

And actually more to the point, you've got it backwards. The SRB failure on Challenger was slow, more like a blowtorch. The explosion was when it compromised the external tank (which, obviously, stored liquids).

Solid propellants aren't like explosives. More to the point, you have to keep them under pressure to get the sort of burn rate that is desired for a rocket.

Comment Re:Speaking of delays... (Score 2) 107

Could you remind me how many people SpaceX has killed? Boeing and Lockheed have certainly killed people in the past.

If you're referring to the AMOS 6 ground failure, ignoring that part of the whole point of flying a stack unmanned as much as you can before you fly it manned is to shake out any problems, is that a manned mission would have almost certainly survived that. Unless the launch escape system failed, despite the drama, that was an eminently survivable. How do we know this? Because AMOS-6's hypergolic propellant tanks didn't ignite until the satellite hit the ground. AMOS-6 had the fairing as some extra protection, but on the other hand, the satellite itself isn't nearly as durable as a crew dragon.

The launch escape system ignites within milliseconds of a failure being detected and almost immediately reaches full thrust, accelerating away at 10gs. Here's a graphic of Dragon's abort test superimposed over the AMOS-6 failure. Things like this are the very reason that launch escape systems exist. NASA's last manned space vehicle lacked such a system entirely. And while their design for the Shuttle ultimately wasn't chosen, you know what? Lockheed's proposal didn't have one either. And it had a strong impact on influencing the final Shuttle design outcome.

Slashdot Top Deals

Like punning, programming is a play on words.

Working...